Different kinds of methods are used for position detection for example in mobile equipment environment. Many of them are based on a contact-free detection technology, such as a magnetic field measurement technology, where magnetic field properties on a local User interface environment are measured. Position detection/context sensing on a mobile equipment level enhances user interface functions, where the position detection function performs for example open and close actions (producing typically ON/OFF-signals).
Generally the magnetic field measurement technology has great advantages but also some disadvantages which effects lack of performance for detection. One of the main problems of magnetic field detection technology is offset disturbance or error on measurement range. Offset problem is coming both from internal (inside the component) and external (inside the equipment) sources.
Internal error affecting to an offset has only a local term, and the error does not typically depend on a position of moving parts. Internal error may be normalized, especially if it is linear and symmetric, but it can still reduce a measurement dynamic range. Moreover the saturated offset could be a fatal error. Temperature may also affect an internal error, which may be normalized especially if it is linear or well-known nonlinear-type. In addition a noise may be one internal error type. A noise is typically not possible to normalize, but effect of the noise can be reduced with sample statistics (filtering). However it can be said that the noise reduces a measurement dynamic range.
External disturbance affecting to an offset has also a local term (inside the equipment) but also a global term, such as Earth's magnetic field, which is weak but needs to take care. Also steady magnets, electric motors, speakers and power lines are possible external error sources and their effects depend on a position to an error source. Offset type changes can possibly be normalized. In addition a noise may also be an external error type, which typically relates environmental like magnetic field changes. Typically it can't be normalized, but effects of noise can be reduced for example with sample statistics (filtering) if error trend is quite slow.
In addition it should be noted that a wide offset variation potential reduces a distance and direction measurement performance.
Stronger magnetic field density will solve many of the problems mentioned above but it is not reasonable because magnetic field can for example destroy or reset the credit card magnetic strips or disturb other electronic devices and their operations. Moreover the problem disclosed above can also be solved with adapting the existing offset level. This however affects inaccuracy for detection when offset level changes. This also affects needs for calibration during function usage.
Therefore, the continuous position detection/context sensing with magnetometer technology will strongly need an appropriate method for reliable and sharp offset effects compensation and error minimization. Especially the need exist for a solution to prevent or minimize disadvantages of magnetic field measurement on local environment.